AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS3-WeA

Paper SS3-WeA7
Does Adsorbed Oxygen Change the Electron Density in Cu?

Wednesday, October 4, 2000, 4:00 pm, Room 210

Session: Surface and Interface Structure I
Presenter: E.F. McCullen, Tufts University
Authors: E.F. McCullen, Tufts University
C.-L. Hsu, Tufts University
R.G. Tobin, Tufts University
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We present new evidence that thin Cu films can have significantly lower conduction electron density n than pure bulk Cu, and that the resistivity increase caused by oxygen adsorption is due in part to a further reduction in n. This finding contradicts the prevailing model of adsorbate-induced resistance, which attributes the resistance increase to electron scattering. In a series of experiments we measured simultaneously the infrared reflectance and dc resistance changes of epitaxial Cu(100) films during oxygen dosing. Earlier experiments challenged the scattering model by showing that the reflectance-resistance change ratio is adsorbate-dependent.@footnote 1@ Adsorbate-induced changes in n could account for the results, but only if n in the films was significantly below the bulk value. The present work shows that the films indeed have reduced electron density. We find that the reflectance-resistance change ratio for adsorbed oxygen depends upon the clean-film conductivity, which varies from sample to sample. This dependence can be understood if the variations in clean-film conductivity are due in part to variations in n. We use these data to set limits on the films' electron density. The results are consistent with a model in which the resistance change produced by oxygen is caused by equal contributions from scattering and reductions in n, and in which each oxygen atom localizes about two conduction electrons. @FootnoteText@ @footnote 1@ E.T. Krastev, D.E. Kuhl and R.G. Tobin, Surf. Sci. Lett. 387, L1051 (1997); C.-L. Hsu, E.F. McCullen and R.G. Tobin, Chem. Phys. Lett. 316, 336 (2000).